The invention relates to power switching semi-conductors, and more particularly to power MOSFETs (metal oxide semiconductor field effect transistors), and the like.
The present invention relates to an improved gating technique providing increased OFF state voltage blocking capability in AC power FET structure such as shown in copending application Ser. Nos. 390,562, and 390,479, filed June 12, 1982, and Ser. No. 421,931, filed Sept. 23, 1982. These Applications disclose lateral FET structure for bidirectional power switching, including AC application. Laterally spaced source regions and channel regions have a common drift region therebetween. Upon application of voltage of either polarity across main terminals connected to the source regions, current flow in either direction is controlled by the potential on split gate electrode means proximate the channels.
The present invention provides a gating technique during the OFF state for preventing minority carrier injection and bipolar action. During the OFF state, one of the channels is gated ON to short an otherwise forward biased junction between the one channel-containing region and the drift region, to prevent minority carrier injection. The OFF state blocking voltage is dropped across the reversed biased junction between the drift region and the other channel-containing region. The OFF state blocking voltage is higher without the forward biased injection junction and the bipolar action therefrom.
The gating ON of the one channel during the OFF state also attracts given polarity carriers in the drift region adjacent the one channel to prevent unwanted inversion to the other polarity type along an induced depletion path through the drift region. This further enhances OFF state voltage blocking capability.